Thermostat with built-in circuit breaker

ABSTRACT

A thermostat assembly which normally opens and closes an electrical circuit over a predetermined temperature range, and which provides a circuit breaking member to break the circuit in the event the circuit remains closed even though the upper temperature limit has been exceeded. Fixed and movable contact arms, alternately opened and closed by the action of a temperature sensitive bimetal member, are mounted on a stack which is suspended from a plate. A safety means in the form of a fusible element is mounted on the plate in the path of movement of the movable arm. In the event the contacts do not separate when the upper temperature limit is exceeded, the movable arm continues to move in the same direction and engages the fusible element, producing a short circuit and causing the fusible element to burn out, thereby to open the circuit.

United States Patent [72] Inventor Melvln J. Rose 3,158,715 11/1964lngwersen 337/125 Athens, NY. 2,790,046 4/1957 Richardson et a1. 337/355; 52 I970 Primary Examiner-Bernard A. Gilheany t d 1971 AssistantExaminer-F. E. Bell I l d e Attorney-James and Franklin [73] AsslgneeAmerican Thermostat Corporation South Cairo, N.Y.

|54| THERMOSTAT WITH BUILTJN CIRCUIT ABSTRACT: A thennostat assemblywhich normally opens "REAKER and closes an electrical circuit over apredetermined tempera- (-hhm' 4 Damn ture range. and which provides acircuit breaking member to a break the circuit In the event the circuitremains closed even [5-] Unh. Ll 337/35, though the upper temperaturelimit has been exceeded. Fixed 5 I I 337/4' 337/97' 337/!25 and movablecontact arms, alternately opened and closed by l l l Ill. C 01h 85/00the action of a temperature Sensitive bimetal member, are [50] Fltld 0'Search 337/4, 3, mounted on a Stack which is suspended from a plate. Asafety 35; means in the form ofa fusible element is mounted on the plate317/16; 219/517 in the path of movement of the movable arm. 1n the eventthe [56] Rdennces Cited contacts do not separate when the uppertemperature limit is exceeded, the movable arm continues to move in thesame UNITED STATES PATENTS direction and engages the fusible element,producing a short 2,085,013 6/1937 Gr y 33 /103 circuit and causing thefusible element to burn out, thereby to 2,598,878 6/1952 Ballou 3371103open the circuit.

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1 TI-IERMOSIAT WITH BUILT-IN CIRCUIT BREAKER It has been common practiceto provide electric devices and appliances with thermostats toalternately open and close the electric circuit, thereby to regulate theappliance operating temperature. Such thermostats have generallyconsisted of fixed and movable contacts, with the movable contact beingacted upon by a heat sensitive element. Such an element can be a bimetalmember, the component metals of which have different coeflicients ofthermal expansion. Increases in appliance temperature normally causethis member to deflect and consequently drive the movable contact in alike direction. While this type thermostat is generally dependablethrough a range of temperatures, it sometimes happens that the contactsweld together. If this occurs, the thermostat will not open theelectrical circuit, and as a result a dangerous overheating situationoccurs which may ruin the appliance or, the more extreme situation,result in a dangerous fire.

The present invention notably supplements the prior art by providing athermostat normally effective to open and close an electrical circuitover predetermined temperature range, in combination with a built-incircuit breaking member which functions in the event that the thermostatfails. The thermostat and circuit breaking member are arranged in asimply constructed, inexpensive but reliable unit, which providesdependable operation within a predetermined temperature range, and whichensures against dangerous overheating.

It is the prime object of the present invention to provide a thermostatto alternately open and close an electrical circuit over a predetenninedoperating temperature range, in combination with a circuit-breakingmember which will break the circuit should the temperature upper limitbe exceeded.

It is a further object of the present invention to provide acircuit-breaking member in combination with a thermostat, wherein thecircuit-breaking member will break the circuit upon the onset of anadjustable present temperature.

It is an additional object of the present invention to provide athermostat in combination with a circuit-breaking member in aninexpensive, compact and reliable assembly.

The present invention provides a thermostat in combination with acircuit breaking member. The thermostat comprises fixed and movablecontact arms mounted on a stack, with a temperature responsive bimetalstrip acting on the movable arm. Upon increase in temperature, thebimetal strip deflects, consequently moving the contact on the movablearm out of engagement with the contact on the fixed arm. Under certainoperating conditions the arm may fail to separate. To take care of thiscondition a circuit-breaking safety means here shown as a fusibleelement, is mounted on a plate from which the stack is suspended. Thefusible element is mounted in the path of travel of the movable arm, andis operatively connected in the electrical circuit. Should the contactsfail to separate at the predetermined temperature any furthertemperature rise causes the bimetal strip to continue to deflect,thereby moving the arms and their engaged contacts toward the fusibleelement. Increasing temperature results in continued movement of thearms until the movable arm engages the fusible element. This engagementshorts the circuit, causing the fusible element to burn away, therebybreaking the circuit.

To the accomplishment of the above, and to such other objects as mayhereinafter appear, the present invention relates to a thermostatassembly as defined in the appended claims, and as described in thespecification taken together with the accompanying drawings in which:

FIG. I is an elevational view of a preferred embodiment of the presentinvention showing the contacts disengaged;

FIG. 2 is a top plan view of the assembly shown in FIG. 1;

FIG. 3 is an elevational view of an alternative embodiment of thepresent invention showing the contacts engaged; and

FIG. 4 is a top plan view of the embodiment shown in FIG.

Referring to FIG. 1, there is illustrated a preferred embodiment of thepresent invention generally designated by the numeral 10. The plate 12,shown in FIG. 2 as being generally rectangular in shape, has a stack 14suspended from one end thereof, that stack being preferably fabricatedfrom an electrically nonconductive and refractory material.

Mounted in any suitable manner on the central portion of the stack 14 isthe fixed arm 18, and the movable arm 16, the movable arm 16 beinginterposed between the fixed arm 18 and the plate 12. Both the fixed arm18, and the movable arm 16, are resilient (that fixed arm being biasedtoward that movable arm) and electrically conductive, and have at outerends thereof terminals (on the movable arm) and 17b (on the fixed arm).The terminal 17a is integral with the movable arm 16 and is adapted tobe connected to one side of the line of an electrical circuit such asthe plus side of battery 15. The terminal 17b integral with the fixed'arm 18, may be cdnnected to one side of the resistance 19 of anelectrical appliance. The arm 16 may be resiliently biased downwardly,while the arm 18 is resiliently biased upwardly.

As best illustrated in FIG. 1, a protruding contact 20b is mounted onthe free end of fixed arm 18. Directly above that contact, and spacedtherefrom, is a contact 20a on the movable arm 16. The movable arm 16extends beyond the contact 20a in the form of an integral extension 22,finally tenninating in the lip 24, the function of which will beapparent as the description progresses.

Suitable mounted on the stack 14 is a bimetal strip 26 which is longerthan the fixed arm 18, but shorter than the movable arm 16, and has aninsulator 28 attached to and extending up from its free end. Undernormal operation within a selected temperature range (thepredetermination of which will be discussed at a later point), when thecontacts 200 and 20b are engaged, an electrical circuit is completedfrom the line terminal 17a, through the movable arm 16 to the contact2041, and then via contact 20b through fixed arm 18 to terminal 17b, andfinally through the appliance resistance 19. As the current flows, theappliance temperature rises accordingly. Rising temperature causes thebimetal strip 26 to deflect upward toward the plate 12. The insulator 28accordingly acts on the movable arm 16 deflecting it about the fulcrum160. When the upper limit of the temperature range is reached, the movable arm 16 will have normally deflected sufficiently for the contact 20ato have fully separated from the contact 20b, thus opening the circuitthrough the appliance resistance 19. While the circuit remains open, theappliance temperature decreases. This decrease in temperature permitsthe bimetal strip 26 to relax some of its deflection causing theinsulator 28 to move downward. The deflection of the movable arm 16 isthereby likewise relaxed, and as it pivots downward about its fulcrum16a, contact 20a engages contact 20b, thereby closing the circuitthrough the resistance 19. As the current flows through the circuitagain, there is a resulting temperature in crease, and the cycle repeatsitself through the nonnal operation of the appliance. In this manner,the appliance temperature is carefully regulated under normal operatingconditions.

Under certain operating conditions, however, the contacts 20a and 20bmay fail to disengage upon the onset of the temperature upper limit.Should the contacts 20a and 20b weld together, the circuit through theappliance will remain closed and additional heating will result. Undersuch conditions, the bimetal strip 26 will continue to deflect upwardlysuch that the insulator 28 will rotate the movable and fixed arms 16, 18about their respective fulcrums 16a, 18a in' a clockwise direction asviewed in FIG. 1. The excessive temperature rise may result in permanentdamage to the appliance, or may produce a dangerous electrical fire.

To prevent such a situation, there is provided on the under sideof plate12 a circuit-breaking member in the form of a resilient fusible element30 mounted on the electrically conductive bosses 34. That fusibleelement is mounted in the path of movement of the extension 22, and isoperatively connected in the electrical circuit by means of the linetenninal 31b and resistance terminal 31a which are connected to thebosses 34 by means of the screws 35 which are received in the holes (notshown) in the bosses 34. The path of the current is from the lineterminal 17a through the appliance resistance 19 to resistance terminal31a, through the fusible element 30, and finally to line terminal 31b,that in turn being adapted to be connected to the negative side ofbattery. 15. As the current continues to flow, the arms l6, 18 continueto rotate clockwise until the lip 24 contacts the fusible element 30.This producesa short circuit, which causes the fusible element 30 toburn out, thus terminating the flow of current in the appliance.

The operating temperature range.of the arms 16, 18 and bimetal strip 26combination, and the temperature at which the lip 24 engages the fusibleelement 30, are both adjustable. The former adjustment is accomplishedin a conventional fashion by providing a shaft 38 having a threadedsection 44 which is received in a hole 45 in the plate 12. The threadedsection 44 terminates in an insulating finger 46 which depends towardand engages the substantially horizontal platform 48 on the fixed arm18. The shaft 38 can be rotated such that it travels downward, causingthe finger 48 to bear against the platform 48, thereby rotating thefixed arm 18 counterclockwise about its fulcrum 18a. Thus, the normalposition of the contact 20b can be varied, producing engagement anddisengagement of the contacts 20a and 20b at temperatures as desired.For example, if the normal location of contact 20b is raised by movingthe shaft 38 upward, the contacts 20a and 20b will engage and disengageat a higher temperature. Similarly, if the shaft 38 is lowered, therebymoving the contact 20b to a lower position, the contacts 20a and 20bcannot engage until the temperature has reached a lower value.

To prevent the fixed arm 18 from being adjusted to either an abnormallylow or high position, the shaft 38 is provided with a rotation stop 42which engages the post 36 which extends from the top of plate 12. Thatrotation stop is fixed to the shaft 38 just above the threaded section,and is of a disc shape with a projecting extension 50. The sides of thatextension (seen best in FIG. 2) engage the post 36, and thereby limitthe permissible downward and upward travel of shaft 38.

The adjustment of the short circuit temperature is effected by providinga screw 32 in a hole 33 in the plate 12. The hole 33 is directly abovethe fusible element 30, and the screw 32 bears against the fusibleelement 30 along its central portion. The screw 32 forces the fusibleelement 30 to bend downward toward the lip 24. Since the amount ofdeflection the strip 26 must undergo is a function of the distancebetween the lip 24 and the fusible element 30, the greater the bend ofthe fusible element 30, the lesser the distance between that fusibleelement and the lip 24, and consequently the lower the circuit breakingtemperature. Conversely the greater the distance between that fusibleelement and the lip 24, the higher must be the temperature before thecircuit is broken.

An alternative embodiment of the invention is illustrated in FIGS. 3 and4. The fixed arm 54 and movable arm 56 are connected at opposite sidesof the housing 52, and extend toward each other. The contacts 55a and55b on the movable and fixed arms 56 and 54 respectively, engageanddisengage in the same manner as in the previous embodiment, due to thedeflection of the bimetal strip 58. The safety means 76 again in theform of a fusible element 78 (FIG. 4) is connected on the top of thehousing 52 by means of the line terminal 31a and resistance terminal31b. Contiguous the fusible element 78, and directly therebeneath, isthe contact 80 which is inserted in a hole 81 in the housing 52. Pressfit into hole 81 and on to contact 80, is a mating female" contact 82.In the event the contacts 55a, 55b weld together, the bimetal strip 58will drive the arms 54, 56 upwardly, such that the lip 57 will engagecontact 82 producing a short circuit, and as in the previous embodimentthe fusible element 78 will burn away so as to break the circuit.

Adjustment of the normal operating temperature range of theappliance inthis embodiment, is accomplished by providing registering holes 64, 66in the housing 52 and the fixed arm 54 respectively. The fixed arm 54 isdownwardly biased, and a screw 62 is inserted into those registeringholes. The head of that screw bears against the top of housing 52 andprevents the arm 54 from rotating counterclockwise due to its bias. Asthe screw 62 is rotated so as to move downwardly through the arm 54,that arm is raised, thus lifting the normal position of the contact 55b,and the temperature at which those contacts engage is thereby raised.

The present invention, therefore, provides an inexpensive and reliablethermostat assembly of simple construction, for regulating the flow ofcurrent through an appliance over a predetermined temperature range, andensures against dangerous overheating or possible fire. Thecharacteristics of adjustable operating temperatures provide thisassembly with a high degree of utility.

While but two embodiments of the present invention are herein disclosed,it will be appreciated that many variations may be made in the detailsthereof, without departing from the spirit and scope of the invention asdefined in the appended claims.

I claim:

1. A thermostat assembly comprising a support, circuit means on saidsupport adapted to be connected to an external circuit and effective toopen and close said circuit, temperature sensitive means on said supportmovable in a given direction upon increase in temperature and active onsaid circuit means to move it in said given direction and to open saidcircuit when said means has been moved to a given position, and safetymeans on said support located beyond said given position in the path ofmovement in said given direction of said circuit, said safety meansbeing adapted to be operatively connected to said electrical circuit andeffective when engaged by said circuit means to open said circuit.

2. The thermostat assembly of claim 1, said circuit means comprising afixed contact and a movable conductive ann adapted to be electricallyconnected in said electrical circuit, said temperature sensitive meansbeing active on said arm to move the latter.

3. The thermostat assembly of claim 2, in which said safety meanscomprises an electrically conductive fusible element.

4. The thermostat assembly of claim 3, said support comprising a plateand a stack assembly attached thereto.

5. The thermostat assembly of claim 4, in which said fixed contact andmovable arm are mounted on said stack assembly.

6. The thermostat assembly of claim 4, in which said fixed contact isresilient and biased toward said movable arm.

7. The thermostat assembly of claim 4, in which said movable arm isinterposed between said fixed contact and said plate.

8. The thermostat assembly of claim 4, in which said fusible element isattached to said plate and is exposed to said movable arm as the lattermoves in said given direction.

9. The thermostat assembly of claim 4, said temperature sensitive meanscomprising a bimetal member.

10. The thermostat assembly of claim 9, in which said bimetal member ismounted on said stack assembly.

11. In the thermostat assembly of claim 1, adjustment means operativelyconnected to said safety means and active to adjustably position ittoward and away from said circuit means.

12. The thermostat assembly of claim 11, in which said safety meanscomprises a fusible element and said circuit means makes electricalconnection thereto when it engages therewith.

13. The thermostat assembly of claim 12, in which said fusible elementcomprises a bendable part exposed to said circuit means, said adjustmentmeans comprising means movably mounted on said support, engageable withsaid bendable part, and effective when moved relative to said support tocause said part to bend toward or away from said circuit means.

14. The thermostat assembly of claim I, said support comprising a-plateon the undersurface of which said safety means is mounted, said circuitmeans comprising fixed and movable contacts mounted on a stack assemblydepending from said physical engagement therewith.

16. In the thermostat of claim 15, means carried by said plate,operatively connected to said strip, and effective to adjust theposition of said strip toward and away from said movable contact.

17. In the thermostat of claim 14, means carried by said plate,operatively connected to said safety means, and efi'ective to adjust theposition of said safety means toward and away from said movable member.

1. A thermostat assembly comprising a support, circuit means on saidsupport adapted to be connected to an external circuit and effective toopen and close said circuit, temperature sensitive means on said supportmovable in a given direction upon increase in temperature and active onsaid circuit means to move it in said given direction and to open saidcircuit when said meaNs has been moved to a given position, and safetymeans on said support located beyond said given position in the path ofmovement in said given direction of said circuit, said safety meansbeing adapted to be operatively connected to said electrical circuit andeffective when engaged by said circuit means to open said circuit. 2.The thermostat assembly of claim 1, said circuit means comprising afixed contact and a movable conductive arm adapted to be electricallyconnected in said electrical circuit, said temperature sensitive meansbeing active on said arm to move the latter.
 3. The thermostat assemblyof claim 2, in which said safety means comprises an electricallyconductive fusible element.
 4. The thermostat assembly of claim 3, saidsupport comprising a plate and a stack assembly attached thereto.
 5. Thethermostat assembly of claim 4, in which said fixed contact and movablearm are mounted on said stack assembly.
 6. The thermostat assembly ofclaim 4, in which said fixed contact is resilient and biased toward saidmovable arm.
 7. The thermostat assembly of claim 4, in which saidmovable arm is interposed between said fixed contact and said plate. 8.The thermostat assembly of claim 4, in which said fusible element isattached to said plate and is exposed to said movable arm as the lattermoves in said given direction.
 9. The thermostat assembly of claim 4,said temperature sensitive means comprising a bimetal member.
 10. Thethermostat assembly of claim 9, in which said bimetal member is mountedon said stack assembly.
 11. In the thermostat assembly of claim 1,adjustment means operatively connected to said safety means and activeto adjustably position it toward and away from said circuit means. 12.The thermostat assembly of claim 11, in which said safety meanscomprises a fusible element and said circuit means makes electricalconnection thereto when it engages therewith.
 13. The thermostatassembly of claim 12, in which said fusible element comprises a bendablepart exposed to said circuit means, said adjustment means comprisingmeans movably mounted on said support, engageable with said bendablepart, and effective when moved relative to said support to cause saidpart to bend toward or away from said circuit means.
 14. The thermostatassembly of claim 1, said support comprising a plate on the undersurfaceof which said safety means is mounted, said circuit means comprisingfixed and movable contacts mounted on a stack assembly depending fromsaid plate, and means resiliently urging said movable contact againstsaid fixed contact, said temperature sensitive means comprising abimetal strip mounted on said stack assembly and engageable with saidmovable contact as said strip moves in said given direction, said givendirection being toward said plate, said movable contact having a partwhich, as said movable contact is moved in said given direction, engagessaid safety means.
 15. The thermostat of claim 14, in which said safetymeans comprises a strip of conductive fusible material, said movablecontact making electrical connection thereto when making physicalengagement therewith.
 16. In the thermostat of claim 15, means carriedby said plate, operatively connected to said strip, and effective toadjust the position of said strip toward and away from said movablecontact.
 17. In the thermostat of claim 14, means carried by said plate,operatively connected to said safety means, and effective to adjust theposition of said safety means toward and away from said movable member.